1. Field of the Invention
The present invention relates to a support moment control method for a leg motion support orthosis put on a person to support the motion (walking or the like) of his or her legs.
2. Related Background Art
Conventionally, there is an already known leg motion support orthosis disclosed in Japanese Patent Laid-Open No. 2003-220102 (hereinafter, referred to as “patent document 1”) as this type of leg motion support orthosis. In the support orthosis in the patent document 1, a waist support belt to be put on a person's waist is coupled to each foot support portion where the person's foot portion is placed, via a waist moment generator corresponding to a hip joint, a thigh support beam corresponding to a thigh, a knee moment generator corresponding to a knee joint, a shank support beam corresponding to a crus portion, and a heel moment generating section corresponding to an ankle joint in this order from the waist side of the support orthosis. Moreover, in the support orthosis of the patent document 1, the foot support portion, the shank support beam, and the thigh support beam are connected to the foot portion, the crus portion, and the thigh portion of the person's leg by using belts, respectively. Then, external forces acting on the person's leg are calculated from detected values of a load sensor provided on the bottom face of the foot support portion and force sensors provided in the belts, and moments generated at the joints of the person's leg are calculated based on the calculated external forces. Moreover, target moments are determined by multiplying a predetermined reduction ratio by the calculated moments to control the moment generators in such a way that forces satisfying the target moments are applied from the support orthosis to the person's leg.
Incidentally, the leg motion support orthosis put on a person is desirably capable of supporting the person's leg motion in such a way that the person is not aware of an inertia force generated by the weight of the support orthosis or a motion thereof. For example, supposing that the target support moments to be applied from the support orthosis to the joints of each leg are each zero, it is desirable that the person can make his or her leg motion in the same manner as when the person is not wearing the support orthosis. In other words, supposing that the target support moments are each zero, the support orthosis is desirably capable of making a motion in such a way as to follow the person's leg motion autonomously (independently) without the need for the person to consciously generate forces to move the respective portions of the support orthosis. On that basis, it is desirable that the support orthosis is capable of making a part of the moments of the leg joints kinetically required to make a desired leg motion that the person is supposing when the person is not wearing the support orthosis.
In the support orthosis of the patent document 1, however, no consideration is given to the external forces applied to the support orthosis 1 necessary for the support orthosis to autonomously follow the person's leg motion and joint moments of the support orthosis. Therefore, when using the support orthosis of the patent document 1, the person receives inertia forces (inertia forces other than support forces) generated by the weight of the support orthosis or the motion of the support orthosis in various situations while the person is moving. Thus, the person wearing the support orthosis often encounters a situation where he or she have to make a leg motion with being aware of the weight of the support orthosis or the like. Consequently, the support orthosis is susceptible to a difference between the actual leg motion pattern and the motion pattern supposed by the person. Furthermore, it leads to causing a jerky leg motion or to making it hard to make a smooth leg motion disadvantageously.
Moreover, since the support orthosis of the patent document 1 has a lot of force sensors provided on the bottom face of the each foot support portion and on the bands fixed to the person's leg, it is disadvantageous in cost and has a problem that it is susceptible to noise included in outputs of the force sensors synergistically. Particularly, the output of the load sensor on the bottom face of the foot support portion is directly susceptible to the influence of the floor shape or the like and the load sensor is easily damaged by an impact on the foot support portion, by which it is hard to secure high reliability. As a result, the moments generated by the moment generators of the support orthosis are easily disordered, which could lead to an abrupt change in the support forces applied to the person's legs.